This invention relates to machine tools and is concerned with mounting of work holders on a machine tool spindle and the operation of the work holder when so mounted.
It is known to provide a work holder with a grip element which can be automatically moved between positions in which it grips and releases the workpiece. It is an object of this invention to provide such a work holder with the facility for being mounted automatically on the spindle so that the work holder can be changed in a numerically controlled machine tool without the need for operator intervention. The need for automatic mounting arises, for example, if one end of the workpiece has been machined and the workpiece has to be turned round to be held by said one end while the other end of the workpiece is machined, said one end, having been machined, usually has a shape or a diameter different from that other end, the latter usually still having the dimension of the original workpiece blank. Therefore a change of work holder is often required before the workpiece can be held at said one end. This applies especially in cases where the work holder is of a type which type is suitable for automatic operation of the gripper elements but usually cannot accommodate large differences in the size of the workpiece.